Metal-poor halo stars as tracers of ISM mixing processes during halo formation

Abstract

We introduce a stochastic halo formation model to compute the early chemical enrichment of the interstellar medium (ISM) of the halo. Contrary to 1-zone chemical evolution models, we are able to resolve local inhomogeneities in the ISM caused by single core-collapse supernovae. These inhomogeneities lead to different element abundance patterns in very metal-poor stars, which can be seen as scatter in the abundances of halo stars with metallicities [Fe/H] < 2.0. The early chemical evolution of the halo proceeds in different enrichment phases: At [Fe/H] -2.0 the halo ISM is well mixed, showing an element abundance pattern integrated over the initial mass function. In the range -3.0 < -4.0. These should be present if the halo ISM started at primordial metallicities and no pre-enrichment by population III stars occurred.